Abstract The authors reviewed the Extracorporeal Life Support Organization (ELSO) data base of all neonates placed on extracorporeal membrane oxygenation for whom CDH was diagnosed between January 1989 and December 1991. For 483 neonates, there were complete data concerning timing of the hernia repair in relation to ECMO. The overall incidence of hemorrhage was 43% (57% among nonsurvivors, 32% among survivors; P < .05). The most common bleeding sites were surgical repair site (24%), head (11.5%), cannulation site (7.5%), and gastrointestinal (5%). Fatal hemorrhage occurred in 4.8% (23 of 483). The most common sites of fatal hemorrhage were head (48%), pulmonary (17%), and abdominal (17%). Bleeding complications were significantly greater for patients repaired on ECMO (58%) versus those repaired before (37%) or after (21%) ( P < .05). Surgical-site hemorrhage requiring transfusion occurred in 38% of those repaired on ECMO versus 18% and 6% of those repaired before and after, respectively ( P < .05). Gastrointestinal and “other” sites of hemorrhage were significantly more common in those repaired on bypass. The number of patients repaired on ECMO increased from 22% to 48% over the 3 years ( P < .05). The incidence of hemorrhagic complications did not differ significantly among the 3 years ( P > .05). Repair of the hernia defect while on bypass was associated with significantly greater bleeding complications. These data should be useful in the planning of future prospective trials.